Under natural viewing conditions, the color and brightness of an object depend on neural signals from both eyes. This research will examine properties of the signals sent from each eye, and of the central mechanisms that combine these signals. Objects seldom are seen in isolation; instead each object is part of a complete visual scene that provides a context in which the object is perceived. It is well known that the color and brightness of an object are affected by light from other objects in view, but very little is known about neural processes that combine each eye's signals that encode information about context. Recent results show that changes in brightness and color appearance caused by a binocularly fused background field, composed of one light presented to the left eye and a corresponding light presented to the right eye, cannot be explained in terms of the adapting effects of (a) the left-eye background alone and (b) the right-eye background alone. This implies that central mechanisms affect normal (two-eyed) color vision in ways that cannot be observed using common experimental procedures that direct lights to only one eye. In this research, both eyes will be stimulated to test fundamental properties of neural signals and central mechanisms that mediate color and brightness perception. A long-term goal of the above research is to provide sensitive and reliable psychophysical techniques to aid in the diagnosis of eye disorders. In a related line of research, a large sample of amblyopes will be studied to detect and quantify brightness deficits in amblyopic eyes, and to determine the relation between brightness deficits and well known deficits in spatial and temporal vision. Interocular brightness matching will be used as a measure of functional luminance level in the amblyopic eye. Then, spatial and temporal sensitivity will be measured in each eye, with the luminance level in the nonamblyopic eye set at a level that matches in brightness the light presented to the amblyopic eye. This research will determine the extent to which functional luminance level can account for spatial and temporal deficits in amblyopia.